Male. Taken at Lardon Chase, Berks, on July 7th 2020. (© David Hastings)
(1/640th sec at f13)

Male underside. Taken at Parkend, Gloucs, on May 7th 2025. (© David Hastings)
(1/1000th sec at /f11)

Female. Taken at Fence Wood, Berks, on August 11th 2021 (© David Hastings)
(1/400th sec at f11)

Female underside. Taken at Hackpen Hill, Oxon., on May 25th 2025. (© David Hastings)
(1/800th sec at f/11)

Mating pair. Taken at Pewsey Downs, Wilts, on June 27th 2023. (© David Hastings)
(1/640th sec at f11)

Description

Family: Polyommatinae

Wing span: 29 - 36 mm

This butterfly is the commonest blue found in the British Isles. The male has violet-blue uppersides, whereas the female is usually primarily brown in colour, with a variable amount of blue on the forewings. Females usually have orange dots on the wing edges, which are absent in the male.

The Common Blue can be found throughout the British Isles, although it is absent from land higher then 1500 ft in Wales and Scotland.

It is found in a wide variety of habitats, including unimproved grassland such as roadside verges and waste ground, downland, woodland clearings, heathland and even sand dunes.

This species has two broods in the southern counties of England, and one brood further north. There may be a third brood in favourable years. In good years, adults may be seen as early as the middle of May on the more southerly sites. These peak at the end of May, giving rise to a second generation that emerges in the second half of July, peaking in the middle of August. The larva is the over-wintering stage.

The main foodplant is Common Bird's-foot Trefoil. Black Medick, Common Restharrow, Greater Bird's-foot Trefoil, Lesser Trefoil and White Clover are also used.

Adults feed primarily on Bird's-foot Trefoil, Bugle, Fleabane, Kidney Vetch, Knapweeds, Marjoram, Ragwort, Thistles, Thyme, Vetches and White Clover.

The Brown Argus and Common Blue can be differentiated from their undersides, since the Brown Argus lacks a spot on the underside of the forewing that is present in the Common Blue. The Brown Argus and female Common Blue can be difficult to tell apart from their uppersides. However, the Brown Argus is completely lacking in blue scales, although it may have a blue sheen. The highly-variable female Common Blue, on the other hand, always has some blue scaling, especially close to the body.

Least Concern

Earliest UK sighting: 27th April ; Latest UK sighting: 28th September

Sightings